I tried searching around for the reason but couldn't find nothing. I thought it was about that stupid Fire Emblem Wiki he persists on contribuitng on but couldn't find nothing there either. There is the chance whatever contributions of his that were found malicious have been deleted but there is no trace at all of it, not even a warning message on his talk page there.
I contacted staff about it, though I can't appeal his block, I hope they will at least tell me why and for how much time he has been blocked (I fear it is an indefinite block just like Luigi).
In the meantime you, TyrantRex and Luigi please calm things down with Grust if needed when he will find out; I am afraid he could decide to quit wikis for good and that would only make the problem worse.